The present invention is directed toward methods of forming openings in doped silicon dioxide. The methods may be used to form self-aligned contact holes and gate structures.
As the size of individual semiconductor devices decreases and packing density increases, the use of self-alignment techniques to relax alignment requirements and improve critical dimension control has become common in semiconductor fabrication. One such technique is called a self-aligned contact (SAC) etch, in which a pair of adjacent gates are utilized to align an etched opening in a doped silicon dioxide layers. The etch used to form the contact opening must often be selective of silicon nitride spacers surrounding the gates. However, when the etch is selective of the silicon nitride spacers, it may not be selective of field oxide regions formed to isolate active areas. If the field oxide regions are etched as a result of a slight misalignment of the mask the, overall performance of the semiconductor device may be degraded.
Thus there remains a need in the art for an etch that is relatively highly selective of doped silicon dioxide layers and relatively minimally selective of silicon nitride and undoped silicon dioxide layers.